The present invention relates to a projection optical apparatus for forming a magnified image of a first object such as a mask onto a second object such as a photosensitive substrate, and to an exposure technique and a device manufacturing technique using such a projection optical apparatus. The present invention further relates to a photomask on which a pattern transferred by the projection optical apparatus is formed and to a method for manufacturing such a photomask.
A projection exposure apparatus, which projects a pattern of a mask (e.g., reticle or photomask) onto a resist-coated plate (e.g., glass plate or semiconductor wafer) using a projection optical system, is used when manufacturing devices such as semiconductor devices and liquid crystal display devices. A projection exposure apparatus employing a step-and-scan method (stepper) has been widely used in the prior art. The step-and-scan projection exposure apparatus performs batch exposure of mask patterns onto a plurality of shot-regions defined on a plate. A step-and-scan scanning projection exposure apparatus, which uses a plurality of small partial projection optical systems having the same magnification, instead of a single large projection optical system has been proposed recently. In the scanning projection exposure apparatus, the plurality of partial projection optical systems are arranged at predetermined intervals in a number of rows along a scanning direction. The scanning projection exposure apparatus exposes patterns of a mask using the partial projection optical systems onto a plate while scanning the mask and the plate.
Each partial projection optical system of the conventional scanning projection exposure apparatus includes a catadioptric system, which forms an intermediate image using for example a concave mirror (or simply a mirror) and a lens, and further includes another catadioptric system. Each partial projection optical system forms an erect image of a pattern of the mask onto the plate with the same magnification.
In recent years, the plates that are used have become large and may have a size of as large as 2×2 meters are increasingly used. When the above-described step-and-scan exposure apparatus, which includes the partial projection optical systems having the same magnification, is used to perform exposure on such a large plate, the mask is also enlarged. A larger mask results in higher costs due to the need to maintain flatness of the mask substrate and the more complicated manufacturing process that becomes necessary when the mask is enlarged. Further, masks in four to five layers are usually necessary to form, for example, a thin-film transistor portion of a liquid crystal display device. This further increases costs. Accordingly, a scanning projection exposure apparatus that can reduce the size of a mask pattern has been proposed (refer, for example, to U.S. Pat. No. 6,512,573). The scanning projection exposure apparatus uses a multiple lens system that includes a plurality of partial projection optical systems having magnifications enabling enlargement instead of equal magnifications. In this scanning projection exposure apparatus, the partial projection optical systems are arranged in two rows in the scanning direction.
However, each partial projection optical system of the conventional enlargement magnification multiple-lens system has an optical axis on the mask and an optical axis on the plate arranged at substantially the same positions. Thus, a pattern exposed onto the plate by a partial projection optical system in one row and a pattern exposed onto the plate by a partial projection optical system in the other row are not continuous with one another.